The present invention relates to a system for controlling an internal combustion engine of the type that has an intake manifold, a throttle valve disposed in the intake manifold for movement between an idle position and a fully opened position, a fuel injection system including at least one electrically actuated fuel injector operative to inject a fuel into an air flow through the intake manifold to form an air-fuel mixture to be sucked into the engine, and an ignition system including a spark plug for igniting charges of the air-fuel mixture in an associated engine cylinder.
A controlling system for an internal combustion engine of the type specified above has been known to include an electrical control unit electrically connected to a fuel injector, a throttle position sensor operative to detect positions of a throttle valve and emit to the control unit an electrical signal representing a detected throttle valve position, an engine speed sensor operative to detect an engine speed and emit to the control unit an electrical engine-speed signal representing a detected engine speed, a temperature sensor operative to detect an engine temperature and emit a temperature signal to the control unit and a mass flow type air flow meter for detecting a mass flow of air sucked through the intake manifold into the engine. The control unit is operative to control the rate of fuel supply through the fuel injection system into the engine in accordance with a first predetermined map of a lattice pattern showing a predetermined relationship between an engine speed and a load value determined on the basis of an detected engine speed and a detected engine intake air flow. The first predetermined map contains a stoichiometrical air-fuel ratio zone below a predetermined load value for a detected engine speed and a power zone above the predetermined load value. The rate of fuel supply controlled in accordance with the first predetermined map is so determined that the engine is supplied with an air-fuel mixture of an air-fuel ratio richer than the stoichiometrical air-fuel ratio when the detected engine speed and load value fall within the power zone in the first predetermined map. The controlling unit is also electrically connected to the ignition system to control the ignition timing in accordance with a second predetermined map similar to the first predetermined map. The ignition timing controlled in accordance with the second predetermined map when the detected engine speed and the load value fall in a stoichiometrical air-fuel ratio zone in the second predetermined map is advanced than in a power zone therein.
This type of engine controlling systems has a problem that an internal combustion engine equipped with the controlling system knocks and tends to be damaged either when an internal combustion engine is operated in a high ambient air temperature as is experienced when an automobile equipped with the engine is operated in a hot district or when the automobile is operated to climb a hill at a high altitude. This is because, under such engine operating conditions, the air sucked into the engine is of a very low density and the engine is at a very high temperature. In such case, the engine throttle valve is widely opened but the engine intake air flow in terms of mass flow measured by the mass flow type air flow meter is at a smaller rate relative to the degree of the throttle valve opening. Accordingly, while the engine is operating at a heavy load condition with the throttle valve widely opened, the engine control by the controlling unit operated in accordance with the first and second predetermined maps is such that the air-fuel mixture and the ignition timing are respectively leaner and advanced than in the heavy load engine operating condition under which the engine is in fact operated.